Starter for a gas discharge lamp, especially a high pressure gas discharge lamp for automobile headlights

ABSTRACT

A starter for a gas discharge lamp, in particular a high-pressure gas discharge lamp for a motor vehicle headlight. The gas discharge lamp is supplied with operating power over the secondary side of a transformer. The required starting power is supplied on the primary side of the transformer and is transferred to the secondary side at the starting time. The starting voltage is generated by a cascade circuit, with the cascade circuit of capacitors and diodes provided in the starter circuit to generate the starting voltage at a charge capacitor. The starter circuit is supplied by the bridge circuit which supplies the gas discharge lamp with power for operation, and for the purpose of starting, the bridge circuit is cycled at a frequency which is much higher than the normal frequency for lamp operation. After the lamp has been started, the bridge circuit is switched to the normal frequency in lamp operation. The starter can be implemented in a two-wire concept, a three-wire concept or a four-wire concept. The starter is connected to the control circuit with two, three or four lines accordingly.

FIELD OF THE INVENTION

The present invention relates to a starter for a gas discharge lamp, inparticular a high-pressure gas discharge lamp for motor vehicleheadlights.

BACKGROUND INFORMATION

In the case of a starter circuit of this type known from German PatentApplication No. 44 23 275, the starting voltage is generated with thehelp of a cascade circuit which increases the voltage, but there is alsoa d.c./a.c. converter connected upstream from the cascade. The expenseof operating the starter in this case should not be underestimated.

In addition, it is known from German Patent No. 40 17 415 that a voltagemay be supplied to the primary winding of a starter transformer in astarting device. The secondary winding of this starter transformer thentransforms this voltage up to the voltage needed to start the lamp. Onthe primary side, a capacitor is arranged in parallel with the seriesconnection of the primary winding and a controllable switch such as acontrolled thyristor. This capacitor is charged to an effective voltagewhich is then applied at this point for the purpose of starting. Onreaching a certain voltage, the controllable switch is enabled and thecapacitor is discharged. With this known starting device, a very highadditional voltage is needed over a separate voltage source to chargethe capacitor.

SUMMARY OF THE INVENTION

The starter according to the present invention for a gas discharge lamphas the advantage that the required starting voltage is supplied easily,is achieved with very inexpensive components, and the starter issupplied with power directly by the control circuit, i.e., the bridgecircuit within the control circuit. This simplifies the starter whilereducing the inductance of the starter. This also yields an improvementin radiant emittance. In addition, the present invention makes itpossible to integrate the starter and the controller, thus permitting afurther reduction in cost and space.

This is achieved according to the present invention by the fact that acascade circuit of capacitors and diodes is provided in the startercircuit to generate the starting voltage at a charge capacitor; thestarter circuit is supplied with power by the bridge circuit whichsupplies the gas discharge lamp with power for operation; the bridgecircuit for starting is cycled at a frequency which is much higher thanthe normal frequency for lamp operation, and the bridge circuit isswitched to the normal frequency for lamp operation after the lamp hasbeen successfully started.

According to especially expedient and advantageous embodiments of thepresent invention, in principle three different embodiments arepossible. This may be a two-wire starter or a three-wire starter or afour-wire starter.

In the case of the advantageous embodiment as a two-wire starter, thestarter is connected to the controller with two lines. In anadvantageous embodiment and an expedient refinement of this embodiment,a switching element, in particular a spark gap, a transistor or athyristor, is provided in series with the primary winding of thetransformer to generate the starting pulse on reaching the startingvoltage on the primary side of the transformer.

In the especially expedient and advantageous embodiment of the starteras a three-wire starter, the starter is connected to the controller bythree lines, with one terminal of the primary winding of the transformerbeing connected directly to the controller without an intermediateswitching element, and the other terminal of the primary winding beingconnected to the output of the cascade. This refinement providesincreased safety plus the possibility of integrating the starter andcontroller.

In another advantageous embodiment of this version of the starter, inthe controller the one directly connected terminal of the primarywinding of the transformer is short-circuited electronically ormechanically to the instrument ground by a switch or a relay providedthere to initiate starting in a controlled manner.

In the case of the advantageous embodiment and refinement of the presentinvention in the four-wire starter version, the starter is connected tothe controller by four lines, where the one terminal of the primarywinding of the transformer is connected to the reference ground of thecontroller by way of a controllable switch, like the one terminal of thecharge capacitor, while the other terminal of the primary winding isconnected to the output of the cascade, and the fourth line is thecontrol line for the controllable switch. In an expedient embodiment, arelay or a transistor or a thyristor may be used as the controllableswitch.

According to an advantageous refinement of the present inventionrelating to all possible embodiment versions, the two-wire version, thethree-wire version or the four-wire version, for starting the bridgecircuit of the controller is operated at a frequency of approx. 20 kHz,and after the lamp has been successfully started, it is switched to anoperating frequency of approx. 400 Hz.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of the starter in an embodiment of thetwo-wire starter according to the present invention.

FIG. 2 shows a schematic diagram of an embodiment of the two-wirestarter according to the present invention, where starting is initiatedby a controllable switching element.

FIG. 3 shows an embodiment of a three-wire starter according to thepresent invention.

FIG. 4 shows a schematic diagram of a starter according to the presentinvention which is connected to the controller by four lines.

FIG. 5 is a graphic diagram, a simulation plot illustrating the voltageramp-up and starting of a starter according to the present invention,where this ramp-up can be seen together with the starting pulse in theupper part of the ramp-up of the cascade voltage and in the lowerdiagram on a smaller scale.

DETAILED DESCRIPTION

FIG. 1 schematically shows the block diagram of a first embodiment ofthe starter designed according to the present invention. This embodimentis a two-wire starter, with the starter connected to the controller overtwo lines and/or terminals 1 and 2. The controller is not shown indetail, nor is the bridge circuit which supplies voltage to the starterat terminals 1 and 2. Thus, the output voltage of the bridge circuit isavailable as an input voltage at input terminals 1 and 2 of the startercircuit. This voltage may be 300 V, for example. Input 1 also formsoutput 5 of the starter circuit, and output 2 is connected by way ofsecondary winding 9 of a transformer 7 to second output 6 of the startercircuit. The gas discharge lamp (not shown) is connected to outputs 5and 6.

The series connection of a charge capacitor C102 and a spark gap F101 isconnected in parallel with primary winding 8 of transformer 7. Adischarge resistor R101 is connected in parallel with charge capacitorC102. To generate the required voltage at charge capacitor C102, acascade circuit composed of capacitors C1 to Cn and diodes D1 to Dn isconnected upstream from the charge capacitor. A charge resistor R102 isconnected to the cathode of first diode D1 and its other terminal isapplied to terminal 2 of the starter. The cascade circuit in successionis designed so that the anode-cathode segment of first diode D1, secondcapacitor C2, the anode-cathode segment of second diode D2, capacitorC3, the anode-cathode segment of third diode D3, fourth capacitor C4 andthe anode-cathode segment of fourth diode D4 are arranged in series withcapacitor C1, and also in a similar manner they are arranged across nextcapacitor Cn and the anode-cathode segment of diode Dn. Charge capacitorC102 is then connected to last capacitor Cn.

The auxiliary starting voltage which is additionally required forstarting is thus not generated in the controller with the presentinvention, but instead is generated with the help of the capacitor-diodecascade formed by capacitors C1 to Cn and diodes D1 to Dn in thestarter. Another advantage is that commercial diodes and capacitors canbe used for the cascade to advantage. In connecting the controller tothe starter, this cascade is connected directly to the output of thebridge circuit which is already present, as illustrated. By cycling thebridge circuit rapidly, the additional auxiliary voltage is generated,as illustrated in detail in the diagrams in FIG. 5.

In order for the additional auxiliary starting voltage to acceleraterapidly, the bridge is cycled at 20 kHz, for example, instead of theusual 400 Hz. The clock frequency of the bridge can be altered through asimple change in program in the microcontroller. After starting, thebridge again operates in the usual start-up and lamp operation mode atan operating frequency of approximately 400 Hz. At this frequency, thecascade is charged slowly, and due to the collapse of the bridgevoltage, which takes place due to the starting of the lamp, the endvalue used for starting is not reached because the lamp is already inoperation.

The rise time and the end value of the additional auxiliary startingvoltage are independent of the bridge voltage applied to inputs 1 and 2,the number of cascade elements 1 through n used, the componentsthemselves, the bridge frequency, charge resistor R102 for limiting thepeak current and any discharge resistor R101 which might be used. Thevoltage rise time of charge capacitor C102 is adjusted with chargeresistor R102, and at the same time the cascade is isolated to a greaterextent for normal lamp operation.

With the present invention, the auxiliary starting voltage is increasedto 1500 V, e.g., at a bridge voltage of 300 V, for example, because ofthe cycling and the cascade in the case of a component number of n=5.The spark gap may then be adjusted to 1200 V, for example, or to a valuebelow 1500 V to initiate starting on reaching this voltage. A ramped-upvoltage of a sufficient level is generated on secondary side 9 with theaid of the transformation ratio of transformer 7.

Due to the possible increase in auxiliary starting voltage which ispossible according to the present invention, it is also possible tochange the transformation ratio of starting transformer 7 so that theseries inductance which is determined by secondary winding 9 can bereduced to an especially favorable value of 1 mH, for example, with asingle-stage starter. Additional advantages derived in addition to thereduction in cost and the space-saving effect include the fact that thetotal efficiency is increased due to the reduction in total power loss,the starting transfer safety is increased, the EMC emission behavior isimproved, and the no-load voltage can be reduced when operating withoutthe starter, thus increasing the safety with regard to hazardousvoltages. In addition, it is possible to allow the no-load voltage tofluctuate in a wider range, so the tolerance requirements here can bereduced.

The embodiment shown in FIG. 2 illustrates another example of thetwo-wire concept of the starter. Instead of a spark gap F101, a MOSFETtransistor 10 is provided and is started by a Zener diode 11 and a gatecharge capacitor 12 on reaching the proper voltage. Gate chargecapacitor 12 is charged across a resistor 13 and has a Zener diode 14 inparallel to limit the voltage.

The version of the two-wire principle illustrated in FIG. 2 forimplementation of the present invention offers the advantage incomparison with the embodiment according to FIG. 1 that starting can beinitiated with greater control. Thus, there is a greater certainty thatthe bridge provided in the controller will have the requiredpreferential direction of polarity at the starting moment so that thelamp will reliably accept it. As in the embodiment in FIG. 1, the inputof the starter in the embodiment in FIG. 2 is cycled at 20 kHz, forexample, at inputs 1 and 2. Diodes D1 to Dn are polarized so that thereis a positive voltage at charge capacitor 20 with respect to thereference ground for generating the starting voltage. As long as thebridge circuit cycles, the polarity of the gate voltage is constantlybeing reversed. A timing element from charge resistor 13 which isconnected at the input to input 1 is adjusted with charge capacitor 12so that the trigger voltage for switch 10 is not reached. The auxiliarystarting voltage reaches the end value after the required charging time.

This charging time is applied adequately and is defined in the controlprogram. After this period of time, the bridge is polarized in thepreferential direction. Thus, the reference potential of switch 10 isthen at −300 V, for example, i.e., −300 V is applied at input 2. Theother pole of the starter, i.e., input 1, is at ground potential andthus represents the positive pole for the starter. Then the timingelement is charged to the trigger voltage with resistor 13 and chargecapacitor 12. Starting occurs after a short delay time. There arevarious options for the switching elements for switch 10, e.g., ahigh-voltage transistor, a field effect transistor, an IGBT or athyristor. It is also advantageous that the N-channel type oftransistors which are preferred can thus be used.

FIG. 3 shows the starter according to the present invention embodied inthe form of the three-wire concept, where the starter is connected tothe controller (not shown) by three lines 1, 2 and 3. The terminal ofprimary winding 8 of transformer 7 is the third line 3 and is connecteddirectly to the controller without an intermediate switching element.The other terminal of primary winding 8 of transformer 7 is connected atthe output of the cascade, the connection point of capacitor Cn andanode of diode Dn. Otherwise, this circuit then corresponds to thecircuit of the starter designed according to the present invention asillustrated in FIG. 1. In this embodiment, a switch which is providedthere and may be designed mechanically as a relay or electronically as atransistor is provided in the controller in an advantageous embodimentto short-circuit the terminal of primary winding 8 directly to theinstrument ground or to the reference potential. Thus, starting isinitiated in a controlled manner. This also has the advantage that whenthe starter is not connected to the controller and the controller is atthe power supply voltage, e.g., the voltage of a motor vehicle battery,there is no voltage on this line 3. This is an essential aspect forincreasing safety. This concept is a good basis for integration of thecontroller and starter.

On the basis of the embodiment illustrated in FIG. 4, the four-wireconcept for the starter according to the present invention isdemonstrated. The arrangement of the components in a cascade, pluscharge capacitor C102, charge resistor R102, discharge resistor R101 andtransformer 7 with primary winding 8 and secondary winding 9 isidentical to the arrangement illustrated in FIG. 1 with the two-wireconcept. The starter illustrated in FIG. 4 is connected to thecontroller by four lines 1, 2, 3, 4. The one terminal of primary winding8 of transformer 7 is connected by a controllable switch 40 to line 3 ofthe controller, where line 3 represents the reference potential of thecontroller or the instrument ground. The one terminal of chargecapacitor C102 and discharge resistor R101 are connected to thereference potential. The control line of switch 40 is connected tofourth line 4 and thus represents the control line of controllableswitch 40. A relay, a transistor or a thyristor may be provided ascontrollable switch 40.

Charge capacitor C102 and the reference ground of controllable switch 40are connected to the reference ground of the controller. This is thecase on line 3. The fourth line 4 is the additional control line for thecontrolled operation of switch 40. In this way, the discharge circuitremains relatively short and at a low resistance and there are no linesto which the higher auxiliary starting voltage is applied, which ensuresgreater safety. In this version, integration of the controller andstarter is implemented in an especially advantageous manner.

The top part of FIG. 5 shows a diagram illustrating a voltage ramp-up onthe diode-capacitor cascade in a simulation plot, namely starting fromthe voltage at 0 V up to approximately −1.5 kV up to the time when thelamp is started. The lower part shows the same curve on a larger scale,where the starting pulse amounting to approximately 20 kV can be seenbetter in its entirety because of the scale, whereas the increase involtage in ramp-up to the starting voltage turns out to be much lowerdue to the scale. Starting is achieved after a ramp-up time of barely 10milliseconds. The upper part of the diagram very clearly shows therelatively high frequency at which the bridge is cycled and accordinglythe voltage curve fluctuates gradually but within a justifiably shortperiod of time up to the starting value.

The advantages achieved on the whole with the present invention,regardless of whether using the two-wire concept, the three-wire conceptor the four-wire concept, include in particular lower costs, fewercomponents and smaller space required. An increase in the totalefficiency and a reduction in total power loss with an increase instarting transfer safety are achieved. The EMC emission behavior isimproved and the no-load voltage is reduced in operation without astarter, which results in a greater safety with respect to hazardousvoltages. Furthermore, the tolerance of the no-load voltage can beexpanded, and starting can be controlled in a controllable manner by asimple function in the software. On the whole, the present inventionpermits integration of the starter and controller, thus yielding afurther reduction in cost and space requirement.

What is claimed is:
 1. A starter for a high-pressure gas discharge lampfor a motor vehicle headlight, the starter being supplied with power bya bridge circuit, the bridge circuit also supplying the gas dischargelamp with operating power, the bridge circuit being cycled for startingat a frequency which is substantially higher than a normal frequency forlamp operation and being switched to the normal frequency for lampoperation after the lamp has been successfully started, the startercomprising: a transformer including a primary winding and a secondarywinding, the secondary winding being supplied with the operating powerof the gas discharge lamp, the primary winding being supplied with arequired starting power, the starting power being transferred to thesecondary winding at a starting time; a charge capacitor; and a cascadecircuit which generates a starting voltage at the charge capacitor, thecascade circuit including a plurality of capacitors and a plurality ofdiodes.
 2. The starter of claim 1, further comprising: a switchingelement, the switching element being in series with the primary windingof the transformer, the switching element generating a starting pulsewhen the starting voltage is reached on the primary winding of thetransformer.
 3. The starter of claim 2, wherein the switching element isa spark gap.
 4. The starter of claim 2, wherein the switching element isa transistor.
 5. The starter of claim 2, wherein the switching elementis a thyristor.
 6. The starter of claim 1, further comprising: twolines, the two lines connecting a controller to the starter.
 7. Thestarter of claim 1, further comprising: three lines, the three linesconnecting a controller to the starter, one of the three linesconnecting a first terminal of the primary winding of the transformerdirectly to the controller without an intermediate switching element;wherein the cascade circuit further includes an output, the output beingconnected to a second terminal of the primary winding of thetransformer.
 8. The starter of claim 7, wherein the line directlyconnecting the first terminal of the primary winding of the transformerto the controller is short-circuited to an instrument ground by one of aswitch and a relay provided at the controller to initiate starting in acontrolled manner.
 9. The starter of claim 1, further comprising: acontrollable switch; and four lines, the four lines connecting acontroller to the starter, one of the four lines connecting a firstterminal of the primary winding of the transformer to a reference groundof the controller by way of the controllable switch, the one line alsoconnecting a terminal of the charge capacitor to the reference ground ofthe controller, another of the four lines being a control line for thecontrollable switch; wherein the cascade circuit further includes anoutput, the output being connected to a second terminal of the primarywinding of the transformer.
 10. The starter of claim 9, wherein thecontrollable switch is one of a relay, a transistor, and a thyristor.11. The starter of claim 1, wherein the bridge circuit of a controlleris operated at a frequency of about 20 kHz, and after the lamp has beensuccessfully started, the bridge circuit is switched to an operatingfrequency of about 400 Hz.